Investigations continue into the relationship of genetic and non-genetic factors in mouse mammary tumorigenesis. Interest is in the different lines of naturally occurring mammary tumor virus (MTV), and the genetically variable inbred mouse strains. Work is also concerned with the manner of transmission of the various MTV's, i.e. whether by female or equally well by either parent. Finally, strains of mice that develop hormone responsive mammary gland tumors and hyperplastic alveolar nodules (HAN), from which malignant mammary tumors arise are also being studied. BIBLIOGRAPHIC REFERENCES: Michalides, R., Vlahakis, G. and Schlom, J.: A Biochemical Approach to the Study of the Transmission of Mouse Mammary Tumor Viruses in Mouse Strains RIII and C3H. Int. J. Cancer 18: 105-115, 1976. Vlahakis, G.: Possible Carcinogenic Effects of Cedar Shavings in Bedding of C3H-AvyfB Mice. J. Natl. Cancer Inst. 58: 149-150, 1977.